1. Field of the Invention
The present invention relates to a power converter control apparatus, which is mounted on mainly a vehicle and is connected to a field winding type rotating generator motor, which operates as a motor at the start of an engine, operates as a generator after the start, and has an armature winding and a field winding.
2. Description of the Related Art
In recent years, for environmental protection and improvement of fuel efficiency, so-called hybrid vehicles including an engine and another power source such as a rotating generator motor have been increasingly developed and put to a practical use. Such vehicles alternatively use the engine or the another power source based on running states.
For example, there is a technique called an idling stop. In order to suppress unnecessary fuel consumption during idling, when a vehicle stops at a traffic light, an internal combustion engine is stopped. When the intention of starting of an operator, such as stepping on the accelerator or brake release is detected, the internal combustion engine is restarted by the rotating generator motor.
The rotating generator motor mounted on such vehicle is mounted on the engine so as to give and receive a torque, and hence an rpm may significantly change by the operator's operation of the accelerator or by the influence of friction of the engine. Therefore, a field winding type, which may be controlled with a field current without embedding a permanent magnet in a rotor, is employed as a type capable of controlling an induced voltage of a rotating generator motor regardless of the rpm of the engine.
When the rotating generator motor mounted on the vehicle is used as a generator, a generation torque corresponding to a power generation amount is generated in the coupled engine. When the rpm is constant, the generation torque increases as the power generation amount becomes larger. Therefore, when the power generation amount is rapidly increased, the generation torque to be generated also rapidly increases. If the acute change of the generation torque occurs during, for example, idling, there may cause an engine stall. Thus, in order to prevent the engine stall during the generation of power, it is necessary to grasp a generation torque amount generated for the engine.
Therefore, for example, JP 421370 B describes that, in order to grasp a load torque during the generation of power, the load torque during the generation of power is estimated based on an rpm of a generator for vehicle, a field current, a battery voltage, and the like.
In general, the generator mounted on the vehicle performs generation voltage control so as to adjust a voltage of a power supply electrically connected to the generator to a predetermined value. However, in this case, if the voltage of the power supply is rapidly changed for some reason, the power generation amount rapidly changes. As a result, the generation torque rapidly changes. If a rapid increase in power generation amount, namely, a rapid increase in generation torque occurs in a state in which an engine output is low, such as an idling state, the engine stall causes. Therefore, it is necessary to estimate the generation torque for the engine during the generation of power and to control the estimated value of the generation torque to a predetermined value. However, there is not a specific condition for the choice between generation voltage control and generation torque control, and hence which control is to be used is a problem.